This invention relates to a foot pedal operated motor control circuit, and more particularly, to such a circuit which employs an inexpensive rotary potentiometer operated by a foot pedal via a helical member.
A variety of motor control devices which are suitable for controlling sewing machines and other small appliances and devices using foot pedals have been proposed or utilized but all suffer the disadvantage of being bulky, expensive, subject to wear, require elaborate linkages, heat up, etc. In such control circuits, the output of the control circuit is applied to a motor for controlling its speed. The control is usually provided by changing the resistance of the control circuit by switching resistors of different values in and out or adjusting the resistance of the particular circuit normally using a potentiometer. The contacts and the resistance elements of such control circuits are subject to wear, arcing, heating and may provide a shock hazard to the user. Furthermore, portions of the control circuit are housed in different units and if potentiometers are used, either the linear or rotary type, elaborate linkages are generally required for converting the linear motion of the foot pedal into a suitable linear or rotary motion for operating the potentiometer. Furthermore, the motor control function may not provide smooth changes in speed, particularly as the contact elements wear or suffer thermal damage. In addition, these controls are sometimes complex and expensive.